1. Field of the Invention
The present invention relates to fans for heat exchangers, and, more particularly, to cooling fans for radiators for internal combustion engines.
2. Description of the Related Art
A cooling fan for an internal combustion engine is typically mounted proximate to a heat exchanger, generally a coolant to air heat exchanger known as a radiator. Often, one or more additional heat exchangers, such as a charge air to ambient air heat exchanger, an exhaust gas recirculation heat exchanger, a transmission oil heat exchanger, a hydraulic oil heat exchanger, or an air conditioning condenser, are mounted in conjunction with the radiator. In order to provide for efficient cooling of these heat exchangers, a fan shroud adjoins the fan side of the heat exchanger combination, which directs cooling ambient air over the entire surface of the heat exchanger, and which prevents inefficient recirculating flow of cooling air through the cooling fan.
The cooling fan is mounted in relation to the fan shroud such that it is located partially within the fan shroud along its axial length, and partially outside the fan shroud. The proportion of the axial length of the cooling fan that is within the fan shroud is referred to as the depth or percentage of fan immersion. The depth or percentage of fan immersion has a large impact on the efficiency of the cooling fan in terms of volumetric air movement for a given amount of power consumption. For a cooling fan for an internal combustion engine that has a rotational speed that is either in a direct relationship to an engine rotational speed, or that has a rotational speed that is entirely fixed, such as an electrically driven fan, and that also has a fixed pitch of its cooling fan blades, the amount of fan immersion may be fixed according to an efficiency that is optimized for the average operating parameters of the machine or vehicle incorporating the internal combustion engine, i.e.—for a given ratio between the machine or vehicle forward speed and engine speed when the machine or vehicle is, for example, in high gear.
It is also known, for example in U.S. Pat. No. 8,408,170 (Kardos, et al), to provide a cooling fan that is moveable axially during vehicle operation, which axial movement is proportionate to the fan speed, which is itself in fixed proportion to the engine speed. Another reference, U.S. Pat. No. 4,387,780 (Fujikawa), describes a cooling fan that is also moveable axially during vehicle operation, with the axial movement being associated with the moveable sheave of a variable speed drive. However, the variable speed drive does not vary the speed of the fan relative to the engine speed, but is merely a variable speed final drive for propulsion of the vehicle, e.g. —a variable speed transmission.
As various machines and vehicles utilizing internal combustion engines and vehicle cooling systems become increasingly efficient, both in terms of fuel efficiency and in terms of exhaust emissions, it is desirable to maximize cooling fan efficiency, in order to move a maximum amount of air with a minimum amount of cooling fan power consumption. The amount of power used to drive a cooling fan is not inconsiderable, and can be as much as seventy horsepower in a large commercial vehicle or similar application. Furthermore, the necessary heat rejection may take place with a heat exchanger or exchangers that are subject to physical size constraints due to aerodynamic or aesthetic considerations. In order to accomplish these ends, it is known to utilize a variable pitch cooling fan.